The quickest way to determine what size the barrel shank is on your rifle is to measure the length of your barrel nut. Standard shank nuts are 7/8" (0.875") in length, whereas large shank nuts are 5/8" (0.625") in length.
https://vortexoptics.com/crossfire-ii-4-12x50-ao-dead-hold-bdc-moa.html
Has a scratch on it. Other than the scratch, really never used it. $210 shipped.